Formation of sheeted cellulose for nitration



M. o. scHuR 1,971,237

FORMATION OF SHEETED CELLULOSE FOR NITRATION Aug. 21, 1934.

Filed Feb. 13, 1931 I W207 w/z a Patented Aug. 21, 1934 rrss sArE NT omen 1 FORMATION OF SHEETED OE LLULOSE FOR NITRATION I Maine Application February 13, 1931, Serial No. 515,578

8 Claims. 01. 260-145) In converting cellulose into nitrocellulose, it is highly important that all the cellulose receive uniform treatment by the nitrating acid. No trouble arises in this connection when the cellulose is cotton linters or is otherwise in finely divided condition, as in the form of shreds, since the nitrating acid readily works its way through the mass when used in excess, as it always is. When, on the other hand, cellulose is converted 10' into nitrocellulose in the form of large sheets of interfelted' fiber, precaution must be taken to ensure access of the nitrating acid to substantially all the sheet surfaces.

With the advent in recent years of refined wood '15 pulps of high alpha cellulose content suitable for nitrocellulose manufacture, what are known as drier sheets of such pulp have appeared on the market- Such sheets constitute an advantageous form in which the pulp manufacturer can put up, store, and shi his product, as all he need do is run off his processed pulp on standard pulp driers capable of handling economicallyenormous quantitles .of pulp per day. They are usually quite thick and rigid as compared with paper, falling properly into the category of boards, rather than papers. For instance, whereas the usual bond papers have a thickness of only about 0.003 inches, drier sheets usually have a thickness of about 0.020 to 0.050 inches.

" The object of the present invention is to provide an economical andeiiicient mode of converting sheet cellulose material of the nature of drier sheetsinto nitrocellulose. I have observed that when drier sheets are steeped in closely-spaced,

: parallel relation in a bath of nitrating acid, there is, as a result of the'buoying action of the acid and other causes, a tendency to bring about facial contact of the" sheets over large areas. Not only does this retard diifusion and penetration of the Z40 nitrating acid into'the contacting portions, but

' quickly dissipated in the main-body of water, hy-

drolysis and loss of nitrocellulose ensues. While it is possible to avoid the foregoing troubles by spacing the sheets sufficiently apart, nevertheless such an expedient is uneconomical, leading, as it 155 does, to the necessity of using greatly enlarged nitrating vats and of having much more of the expensive nitrating acid in actual use in the process.

- Broadly stated, in accordance with the present invention, I maintain the desired high fiber-t0- acid ratio and secure the desired uniformity of nitration by pleating the sheets and nitrating them as a series of juxtaposed sheets, the array in the nitrating bath preferably being such that at most substantially only line or point contact can be established between the sheets In preforming a sheet, which may be done either by hand or by machine, the pulp at the joints of the folds should be practically in no more compacted con- 'dition than the rest of the sheet, as appreciable compression of the pulp at these regions would impede penetration of nitrating acid thereinto. The gentle rolling or wiping of the joints with the fingers when a sheet is folded or pleated by hand does not, however, impair the sheet for nitration.

With the foregoing and other features and objects in view, the present inventionwill now be more fully described in conjunction with the accompanying drawing, wherein Figures 1, 2 and 3 illustrate in perspective dif ferent arrangements of pleatedsheets in accordance with my invention. 7 Figures 4, 5 and 6 represent diagrammatically and conventionally plan views of nitrating vats in which the sheets are shown preformed and prearranged as in Figures 1, 2 and 3, respectively.

Figure 7 is a detail of the joint portion of a properly pleated sheet.

Figure 8 is a plan view of a pleated sheet with dimensions indicated thereon such as might conveniently be used in practice.

Before proceeding to a detailed description of what is shown'by the drawing, it should beunderstood that the drawing is intended as pictorial representations of my invention, and are not working drawings in the sense that they give proper relative sizes or nitrating vats of a capacity which could be used in commercial production. Only those features which go to make up the presentinvention have, for the sake of simplicity, been illustrated, as those skilled in the art; needbe taught only these features to be enabled to apply my invention in actual practice. In Figures 1 and 4, the sheets 1 are shown pleated vertically, the folds being defined by deep, V-shaped flutes 2. The'sheets are of suiiicient rigidity to stand up unsupported on a flat surface, especially since they are stiffened against buckling by the pleats. In orderto preventpossibility of displacement of the sheets inthe nitrating vat 3 to establish area contact therebetween, I preferably insert flat sheets 4 between adjacent pleated sheets, so that at most orfly line contact can take place between sheets. The pleated sheets 1, and so too the unpleated sheets 4, are cut in lengths sufficient to span opposite side walls of the nitrating vat, as shown in Figure 4', whereby collapse of the pleated sheets to fiat condition is restrained by the walls. Instead of spanning opposite side walls of the nitrating vat, the sheets may be stacked ina holder or cage which permits of the rapid intro-' duction into or removal from the nitrating vat of a complete batch of sheets. Upon covering the sheets with a bath of nitrating acid, the flutes 2 afford spacious channels forthe circulation of acid to and from all portions of the bath to substantially all the sheet surfaces.

In Figure 2, I have shown an arrangement in which the sheets are pleated alternatelyin different directions: that is to say, one of the sheets 5 is pleated vertically and the adjacent sheet 6 ispleated horizontally. The horizontally pleated sheet may be supported or hung in the bath of nitrating acid, but mere frictional contact with the vertically pleated sheets, together with the buoyant effect of the nitrating acid may be all that is'necessary to, keep the folds open to the desired degree. Such an arrangement of sheets possesses the advantages that only point contact can be established between adjacent sheets and that large, horizontal channels, 7, as well as vertical channels 8, are created for free flow and diffusion of the nitrating acid to and from the sheet surfaces. Y

The arrangement thus far shown have the common characteristic that the joints of one pleated sheet lie immediately outside the flutes of an adjacent pleated sheet. By providing suitable spacing means which prevent contact between adjacent sheets and aiford ample clearance therebetween for acid movement, it is possible to utilize the fluted spaces of one sheet for receiving the joints of an adjacent sheet, and thus to increase considerably the fiber-to-acid ratio in a bath of nitrating acid of given size. Such a preferred arrangement is illustrated in Figures 3 and 6, wherein a spacing frame 9 is shown located between adjacent, vertically pleated sheets. The frame, which may be made of suitable acid-resistant material, is provided with three spaced horizontal bars 10, of saw-tooth shape, conforming to the configuration of the pleated sheets and engaging the sheets only at their upper and lower marginal areas and centrally, as it is at these localities that there is danger of the displacement of the sheets toward one another. The area of the sheets engaged by the frame is thus comparatively little. The bars 10 should be of substantial width, as shown, in order to safeguard the sheets from touching one another, as well as to leave sufficient space between sheets to permitfree interplay of acid therein with the main body of acid. The bars serve the important function of retaining'the pleats at thedesiredangularity and regularity, that with no collapsing of the pleats toward flat condition or closing of the folds upon one another. Instead of thecomparatively heavy spacersshownin Figure 3, thin, saw-tooth or zigzag strips of material, preferably acid-resistant material, may, be used. Thus, we have found that in sheets 20 inches wide, strips of -so-called Allegheny metal 3/64: of aninch thick, placed about 4 inches from the top of the sheet and, about 4 inches fromthe bottom, are suffi- I cellulose plants equipped to nitrate drier sheets of nevnasv cient to maintain the sheets in correct spacing. It is interesting to note that in many cases it is necessary merely to fit the spacers into the pleats in order to have the spacers stay in place, the friction between the sheet and the metal being all that is necessary to support the horizontal spacers. c.

It is an easy and inexpensive matter to put my invention into immediate practice in nitropulp. In fact, as already indicated, the sheets may be pleated by hand, in which case, as illustrated in Figure 7, the outer layer of pulp 11 on the joints or lines of fold may be torn by the stretching action, whereas the inner layers may be wrinkled by crowding. Or the sheets may be pleated by machine to effect the desired result. The pleated'sheets of nitrocellulose may be finished, stored, and sold as such, and they possess the advantage of greater stifiness or resistance against fracture and disintegration. I therefore claim such sheets of nitrocellulosaas well as the pleated sheets of cellulose and their arrangement, as my invention, as one of the desiderata of sheet nitrocellulose is that it maintain its integrity during handling. An advantage in this connection is the fact that the nitrocellulose itself is stiffer than the original cellulose, and that this stiffness is augmented by the stiffness afforded by the pleats.

, In using the words pleats and pleated as applied to sheet cellulose, I mean to include a wavy or sinuous formation in the sheets, as these are to be construed as mere modifications of a pleated structure wherein the joints are more or less rounded or smooth. By way of illustration, it might be noted that the pleated sheets may be handled conveniently when their pleatsare about two feet long, and, as shown in Figure 8, when their side edges are separated about two feet; the folds about two inches in width; and the lines of fold about inch apart. While other dimensions may be used, in any case the distance between lines of fold should properly be muchless than the width of the folds, in order to get away as far as conveniently possible from flat sheets. The sheets cannot be regarded as paper or paperboard, for they are entirely'free from sizing material, fillers, or other papermaking ingredients. For the best results, only refined wood pulps of pure whiteness and of high alpha cellulose content, for instance 94%, or thereabout, or-other similar cellulose fiber, shouldgo into the manufacture of the sheets in order to insure nitrocelluloses or other cellulose derivatives of the highest quality. Other types of cellulose may, of course, be used, such for example,'as sulphite pulp, cotton, rag stock, and the like.

What I claim is:

1. A process which comprises pleating sheets of cellulose to form a succession of folds defined by deep V-shaped flutes and by lines of fold separated by, a distancemuch less than the depth of said flutes, arranging a series of such sheets in juxtaposed relationship such that adjacent sheets make at most only line contact and are separated from eachother by a distance averaging at least 3/64 inches for their entire confronting surfaces, and covering the sheets with nitrating acid, whereby the heat liberated during the nitrating operation is quickly and uniformly dissipated in the acid occupying the spaces defined by said flutes. i

2. A process which comprises pleating interfelted sheets of cellulose fiber to form a succes- 150 sion of folds defined by V-shaped flutes of a depth in the order of magnitude of at least about two inches and by lines of fold separated by a distance much less than the depth of said flutes, arranging a series of such sheets in juxtaposed relationship such that adjacent sheets make at most only line contact and are separated from each other by a distance averaging at least 3/ 64' said flutes, arranging a series of such sheets in juxtaposed relationship such that adjacent sheets make at most only line contact and are separated from each other by a distance averaging at least 3 64 inches for their entire confronting surfaces, and covering the sheets with nitrating acid, whereby the heat liberated during the nitrating operation is quickly and uniformly dissipated in the acid occupying the spaces defined by said flutes.

4. A process which comprises pleating sheets of cellulose pulp having a thickness of about .020 to .050 inches to form a succession of folds defined by V-shaped flutes of a depth in the order of magnitude of at least about two inches and by lines of fold separated by a distance much less than the depth of said flutes, arranging a series of such sheets in juxtaposed relationship such that adjacent sheets make at most only line contact and are separated from each other by a distance averaging at least 3/64 inches for their entire confronting surfaces, and covering the sheets with nitrating acid, whereby the heat liberated during the nitrating operation is quickly and uniformly dissipated in the acid occupying the spaces defined by said flutes.

5. A pleated sheet of substantially uniformly nitrated cellulose having a thicknes of about .020 to .050 inches, the folds in said sheet being defined by deep, V-shaped flutes and by lines of fold separated by a distance much less than the depth of said flutes.

6. A pleated sheet of substantially uniformly nitrated cellulose having a succession of folds which are defined by V-shaped flutes of a depth in the order of magnitude of at least about two inches and by lines of fold separated by a distance much less than the depth of said flutes.

'7. A pleated sheet of substantially uniformly nitrated cellulose having a thickness of about .020 to .050 inches and having a succession of folds which are defined by V-shaped flutes of a depth in the order of magnitude of at least about two inches and by lines of fold separated by a dis-- tance much less than the depth of said flutes.

8. A pleated sheet of substantially uniformly nitrated cellulose whose folds are defined by deep, V-shaped flutes and by lines of fold separated by a distance much less than the depth of said flutes.

MILTON O. SCHUR. 

